Articles having a surface with low wettability and method of making

ABSTRACT

An article comprises a textured surface disposed on a substrate. The surface has an effective liquid wettability sufficient to generate, with a reference liquid, a contact angle in a range from about 120° to about 180°. The surface comprises a material having a nominal liquid wettability sufficient to generate, with the reference liquid, a nominal contact angle in a range from about 60° to about 90°, the material comprising at least one material selected from the group consisting of a polymer and a ceramic. The properties of the surface may include low-drag or low-friction, self-cleaning capability, and resistance to icing, fouling, and fogging, and the like. Methods of making such a surface are also described.

BACKGROUND OF INVENTION

The invention relates to surfaces having low liquid wettability. Moreparticularly, the invention relates to such surfaces, where the surfaceis characterized by having one or more of the following properties:low-friction properties, self-cleaning capability, and resistance toicing, fouling, and fogging. Even more particularly, the inventionrelates to articles having such surfaces.

The “liquid wettability” of a solid surface is determined by observingthe nature of the interaction occurring between the surface and a dropof a given liquid disposed on the surface. A surface having a highwettability for the liquid tends to allow the drop to spread over arelatively wide area of the surface, thereby “wetting” the surface. Inthe extreme case, the liquid spreads into a film over the surface. Onthe other hand, where the surface has a low wettability for the liquid,the liquid tends to retain a well-formed, ball-shaped drop shape. In theextreme case, the liquid forms spherical drops on the surface thateasily roll off of the surface at the slightest disturbance.

The extent to which a liquid is able to wet a solid surface plays asignificant role in determining how the liquid and solid will interactwith each other. A high degree of wetting results in relatively largeareas of liquid-solid contact, and is desirable in applications where aconsiderable amount of interaction between the two surfaces isbeneficial, such as, for example, adhesive and coating applications. Byway of example, so-called “hydrophilic” materials have relatively highwettability in the presence of water, resulting in a high degree of“sheeting” of the water over the solid surface. Conversely, forapplications requiring low solid-liquid interaction, the wettability isgenerally kept as low as possible in order to promote the formation ofliquid drops having minimal contact area with the solid surface.“Hydrophobic” materials have relatively low water wettability; so-called“superhydrophobic” materials have even lower water wettability,resulting in surfaces that in some cases may seem to repel any waterimpinging on the surface due to the insignificant amount of interactionbetween water drops and the solid surface.

Articles having tailored surface properties are used in a broad range ofapplications in areas such as transportation, chemical processing,health care, and textiles. Many of these applications involve the use ofarticles having a surface with a relatively low liquid wettability toreduce the interaction between the article surface and various liquids.In particular, the wetting properties of a material can be tailored toproduce surfaces having properties that include low-drag orlow-friction, self-cleaning capability, and resistance to icing,fouling, and fogging.

Different methods of reducing drag and friction have been used indifferent applications. To reduce friction in a pipe, for example, pipeshave been made macroscopically smoother. Macroscopic structures, such as‘riblets,’ have been used to create flow patterns that offer reducedresistance to flow. Similarly, ‘compliant’ surfaces that changeadaptively based on flow characteristics have been tried as well. Suchmacroscopic modifications have been able to produce at best a 5-10%reduction in drag.

Hydrophobic surfaces on articles have also been formed using hydrophobicmaterials, such as Teflon®, polymer gels and solutions, and the like.Such materials are typically deposited as a film on a substrate or areformed into the article itself. For example, polymeric solutions areapplied to racing boats to reduce drag, and polymer gels are applied tothe inner surfaces of oil pipelines. Surfaces comprising such materialsgenerally reduce drag or friction by 5-10%. Such coatings are subject torapid wear and are not thermally or chemically stable at highertemperatures.

Current approaches to the production of articles having minimalinteraction with fluids have been focused on applications of limitedscope, and have produced only limited success. Therefore, there remainsa need across several industries for articles having a surface with lowliquid wettability. Moreover, these industries also require methods forproviding such a surface on an article.

SUMMARY OF INVENTION

The present invention meets these and other needs by providing anarticle having a surface with a low liquid wettability. The surfaceprovides properties that may include, as non-limiting examples, one ormore of low-drag or low-friction properties, self-cleaning capability,and resistance to icing, fouling, and fogging.

Accordingly, one aspect of the invention is to provide an article. Thearticle comprises a surface disposed on a substrate, wherein the surfacecomprises

a. a material having a nominal liquid wettability sufficient togenerate, with a reference liquid, a nominal contact angle in a rangefrom about 60° to about 90°, the material comprising at least onematerial selected from the group consisting of a polymer and a ceramic;and

b. a texture comprising a plurality of features;

wherein the surface has an effective liquid wettability sufficient togenerate, with the reference liquid, a contact angle in a range fromabout 120° to about 180°.

Still another aspect of the invention is to provide a method of makingan article. The method comprises

a. providing a substrate and

b. forming a surface on the substrate, wherein the surface comprises amaterial having a nominal liquid wettability sufficient to generate,with a reference liquid, a nominal contact angle in a range from about60° to about 90°, the material comprising at least one material selectedfrom the group consisting of a polymer and a ceramic, and the surfacefurther comprising a texture, wherein the texture comprises a pluralityof features;

wherein the surface has an effective liquid wettability sufficient togenerate, with the reference liquid, a contact angle in a range fromabout 120° to about 180°.

These and other aspects, advantages, and salient features of the presentinvention will become apparent from the following detailed description,accompanying drawings, and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a surface of an article ofthe present invention;

FIG. 2 is a schematic representation of a fluid disposed on a nominallyflat surface;

FIG. 3 a is a photograph of a water droplet on a superhydrophobicpolycarbonate surface;

FIG. 3 b is a micrograph of the superhydrophobic polycarbonate surfaceshown in FIG. 3 a;

FIG. 3 c is a photograph of a water droplet on a nominally flatpolycarbonate surface;

FIG. 4 is a schematic representation of a cross-section of a surface ofthe present invention, showing the texture of the surface;

FIG. 5 is a schematic representation of the formation of a surface ofthe present invention using a plurality of nanoparticles and a polymersolution;

FIG. 6 is a schematic representation of the formation of a surface ofthe present invention by assembling a plurality of nanoparticles in ablock copolymer matrix;

FIG. 7 is an image of a plurality of polystyrene beads deposited onto asubstrate in preparation of making a mold for replicating a surface ofthe present invention;

FIG. 8 is an image of a silicone master mold having a texture on asurface of the present invention;

FIG. 9 is an image of a polycarbonate surface having a texture that wasformed by compression molding the polycarbonate with the silicone moldshown in FIG. 8;

FIG. 10 is a schematic representation of an article of the presentinvention, wherein the article is an airfoil; and

FIG. 11 is a schematic representation of an aircraft turbine thatincorporates at least one article having an icing resistant surface ofthe present invention.

DETAILED DESCRIPTION

In the following description, like reference characters designate likeor corresponding parts throughout the several views shown in thefigures. It is also understood that terms such as “top,” “bottom,”“outward,” “inward,” and the like are words of convenience and are notto be construed as limiting terms. Furthermore, whenever a particularfeature of the invention is said to comprise or consist of at least oneof a number of elements of a group and combinations thereof, it isunderstood that the feature may comprise or consist of any of theelements of the group, either individually or in combination with any ofthe other elements of that group.

Referring to the drawings in general and to FIG. 1 in particular, itwill be understood that the illustrations are for the purpose ofdescribing a particular embodiment of the invention and are not intendedto limit the invention thereto. FIG. 1 is a schematic cross-sectionalview of a surface of an article of the present invention. Article 100comprises a surface 120 disposed on a substrate 110. As used herein, theterm “surface” refers to that portion of the substrate 110 that is indirect contact with an ambient environment surrounding substrate 110.Surface 120 has a low liquid wettability. One commonly accepted measureof the liquid wettability of a surface 120 is the value of the staticcontact angle 140 formed between surface 120 and a tangent 145 to asurface of a droplet 150 of a reference liquid at the point of contactbetween surface 120 and droplet 150. High values of contact angle 140indicate a low wettability for the reference liquid on surface 120. Thereference liquid may be any liquid of interest. In many applications,the reference liquid is water; for instance, in applications focused onreducing the accretion of ice on a surface, the reference liquid issupercooled water (liquid water at a temperature below its freezingpoint). In other applications, the reference liquid is a liquid thatcontains at least one hydrocarbon, such as, for example, oil, petroleum,gasoline, an organic solvent, and the like. As described above, the term“superhydrophobic” is used to describe surfaces having very lowwettability for water. As used herein, the term “superhydrophobic” willbe understood to refer to a surface that generates a static contactangle with water of greater than about 120 degrees. Because wettabilitydepends in part upon the surface tension of the reference liquid, agiven surface may have a different wettability (and hence form adifferent contact angle) for different liquids.

Surface 120 comprises a material that has a moderately high wettabilityfor a given reference liquid, yet surface 120 itself has a substantiallylower wettability for the same reference liquid than that typicallymeasured for the material. In particular, surface 120 comprises amaterial having a nominal liquid wettability sufficient to generate anominal contact angle in a range from about 60° to about 90° with agiven reference liquid. In particular embodiments, surface 120 consistsessentially of the material. For the purposes of understanding theinvention, a “nominal contact angle” 240 (FIG. 2) means the staticcontact angle 240 measured where a drop of a reference liquid 230 isdisposed on a flat, smooth (<1 nm surface roughness) surface 220consisting essentially of the material. This nominal contact angle 240is a measurement of the “nominal wettability” of the material.

Surface 120 further comprises a texture 130 comprising a plurality offeatures 135. The present inventors have found that by providing asurface 120, comprising a material of moderately high nominalwettability, with a texture 130, the resulting textured surface can haveremarkably lower wettability than that inherent to the material fromwhich the surface is made. In particular, surface 120 has an effectivewettability (that is, wettability of the textured surface) for thereference liquid sufficient to generate a contact angle in the rangefrom about 120° to about 180°. Where the reference liquid is water, forexample, the material would be considered to be hydrophilic based on itsnominal contact angle, yet the surface 120, made of textured hydrophilicmaterial, would be considered superhydrophobic due to its high contactangle.

An example of the behavior of a fluid drop on an article of the presentinvention is shown in FIGS. 3 a and 3 b. Surface 304 comprises apolycarbonate, which is hydrophilic. The contact angle formed by waterdroplet 302 and surface 304 is about 130° (FIG. 3 a). The polycarbonatesurface 304 has a texture 306, which can be seen in a top view ofsurface 304, shown in FIG. 3 b. An example of the behavior of a waterdroplet on a flat polycarbonate surface lacking the texture of theprevious example is shown in FIG. 3 c. The contact angle formed by fluid308 and surface 310 is about 80°. In contrast to the texturedpolycarbonate surface 304 shown in FIG. 3 c, the flat surface 310 wassubstantially devoid of any texture or topographical features, such aselevated portions, depressions, and the like.

Surface 120 (FIG. 1) comprises at least one material selected from thegroup consisting of a polymer and a ceramic. Polymer materials that maybe used in surface 120 include, but are not limited to, polycarbonates,including cyclic polycarbonates; polyimides, including cyclicpolyimides; polysilazanes; acrylates, including UV curable acrylates;polyurethanes; epoxies; polyether imides; polysulfones; blockcopolymer/copolymer mixtures; and combinations thereof. Suitable ceramicmaterials include inorganic oxides, carbides, nitrides, and combinationsthereof. Non-limiting examples of such ceramic materials include tinoxide, titania, silicon carbide, titanium nitride, stibinite (SbS₂),zirconia, hafnia, titanium oxynitride, and combinations thereof.

Substrate 110 may comprise at least one of a metal, an alloy, a plastic,a ceramic, or any combination thereof. Substrate 110 may take the formof a film, a sheet, or a bulk shape. Substrate 110 may represent article100 in its final form, such as a finished part; a near-net shape; or apreform that will be later made into article 100.

Surface 120 may be an integral part of substrate 110. For example,surface 120 may be formed by replicating a texture directly ontosubstrate 110, or by embossing the texture onto substrate, or by anyother such method known in the art of forming or imparting apredetermined surface texture onto a substrate surface. Alternatively,surface 120 may comprise a layer that is disposed or deposited ontosubstrate 110 by any number of techniques that are known in the art.

As described above, surface 120 is not a smooth surface, but instead hasa texture 130 comprising a plurality of features 135. The plurality offeatures 135 may be of any shape, include at least one of depressions,protrusions, nanoporous solids, foamed structures, indentations, or thelike. The features may include bumps, cones, rods, wires, channels,substantially spherical features, foamed structures, substantiallycylindrical features, pyramidal features, prismatic structures,combinations thereof, and the like. In certain embodiments, as depictedin FIG. 4, each feature 402 has at least one dimension 404 (for example,length, width, diameter, or thickness) in a range from about 10 nm toabout 50,000 nm. In some embodiments, dimension 404 is in the range fromabout 10 nm to about 10,000 nm, and in particular embodiments dimension404 is in the range from about 10 nm to about 1000 nm. The features 402are spaced from each other by a distance 406 (also referred tohereinafter as a “spacing dimension”); in some embodiments spacingdimension 406 is substantially equal to the dimensions 404 of thefeatures. For example, spherical or sphere-like features, each having adiameter of about 100 nm, are spaced about 100 nm apart. In oneembodiment, the plurality of features 402 is substantially close-packed.The plurality of features 402 may be arranged in either an ordered arrayon surface 408, or in a disordered or random fashion.

The plurality of features 135 (FIG. 1) making up texture 130 need not beconfined to the surface 120 or a region immediately proximate to thesurface 120. In some embodiments, article 100 further comprises a bulkportion 110 disposed beneath surface 120, and the plurality of features135 extends into bulk portion 110. Distributing features 135 throughoutthe article 100, including at the surface 120 and within the bulkportion 110, allows surface 120 to be regenerated as the top layer ofsurface erodes away.

Another aspect of the invention is to provide a method for makingsurface 120 and article 100 described hereinabove. The method comprisesproviding a substrate 110 and forming a surface 120 on the substrate110. Surface 120 comprises a material having a nominal liquidwettability sufficient to generate, with a reference liquid, a nominalcontact angle in a range from about 60° to about 90°, and the materialcomprises at least one material selected from the group consisting of apolymer and a ceramic. Surface 120 further comprises a texture 130comprising a plurality of features 135. As previously described, theresulting surface 120 has a significantly reduced wettability comparedto the nominal wettability of the material: wettability levelssufficiently low to generate, with the reference liquid, a contact anglein a range from about 120° to about 180°.

In one embodiment, shown schematically in FIG. 5, a plurality ofnanoparticles 540 is initially deposited on substrate 510. The pluralityof nanoparticles 540 may have a liquid wettability that is high or low;may be metallic, non-metallic; or a combination of both; and may becoated or uncoated. Nanoparticles 540 may be deposited in either anordered or disordered fashion to form an assembly 542 or array ofnanoparticles on substrate 510. The coverage provided by assembly 542may be limited to a selected area of substrate 510, or complete coverageof substrate 510. In one embodiment, the plurality of nanoparticles 540may be secured or anchored to substrate 510 by heat treating assembly542 at a temperature that will partially melt the particles 540 and fusethem to substrate 510. Following deposition of nanoparticles 540 onsubstrate 510, a polymer solution 550 is then deposited over theplurality of nanoparticles 540 to form a coating 560. Application ofpolymer solution to the plurality of nanoparticles 540 deposited onsubstrate 510 may be by spraying, spin coating, dip coating, or thelike. The polymer solution comprises any of the hydrophilic polymers,such as, but not limited to, those polymers previously described herein.The resulting coating 550 is then heat treated to remove the solvent andensure that the annealed polymer conforms to the underlying structure ofthe nanoparticle clusters. Additional or alternative texture may then beprovided by etching means known in the art, such as, but not limited to,plasma etching, irradiation (particularly with UV light), or solventetching. Such etching selectively removes the polymer.

In another embodiment, the plurality of nanoparticles 540 and polymersolution 550 are blended together and applied to substrate 510 in asingle step using commonly used coating techniques, such as spraycasting, screen printing, roll casting, drop casting, dip coating, andthe like. The nanoparticles comprise from about 0.001 volume percent toabout 50 volume percent of the solution. The resulting coating may thenbe heat treated as previously described to ensure good cohesive andadhesive strength. Additional or alternative textures may then beprovided by etching processes, as previously described hereinabove.

Alternatively, the plurality of nanoparticles 540 is deposited onsubstrate 510 to achieve substantially complete coverage. A monomer,such as a silazane monomer, is then infiltrated into the gaps betweennanoparticles 540. The monomers are then crosslinked by the use ofcatalysts, heat, UV radiation, thermal crosslinking, solvents, and thelike, to provide a robust polymeric coating. An additional oralternative texture may then be provided by etching processes, aspreviously described hereinabove.

In another embodiment, a plurality of nanoparticles 640 are assembled ina block copolymer matrix 600, as shown in FIG. 6. Nanoparticles 640 maybe either coated or uncoated. One of the block copolymers 660 is morecompatible with either nanoparticles 640 or with coatings applied to thenanoparticles, resulting in a self-assembled solution. Upon annealing,the self-assembled solution produces texture 630. An additional oralternative texture may then be provided by etching processes, aspreviously described hereinabove.

The methods of providing texture 130 that have been previously describedabove rely on the formation of at least one coating or layer onsubstrate 110. In other embodiments, texture 130 is provided to orformed directly on a surface of substrate 110. Texture 130 may be formeddirectly onto the surface 120 of substrate 110 by any one ofreplication, embossing, molding or extrusion. In one embodiment, areplicating means such as, but not limited to, a mold or a die, isprovided with a template corresponding to the texture to be provided toa surface. A template of the replicating means is brought into contactwith the surface, thereby imparting texture 130 to the surface.

The formation of texture 130 on a polycarbonate surface 120 isillustrated in FIGS. 7, 8, and 9. In FIG. 7, a plurality of polystyrenebeads 710 are deposited onto a substrate. Deposition of the polystyrenebeads 710 on the substrate may be accomplished by any of the meansdescribed hereinabove. A silicone mold of the beads is then cast, andthe polystyrene beads 710 are removed by dissolution, etching, or thelike, to yield a silicone master mold having a texture, the face ofwhich is shown in FIG. 8. The silicone master mold is then used tocompression mold polycarbonate, where face 820 creates a texture on thesurface of a polycarbonate substrate that corresponds to that of face820. The texture of the polycarbonate surface is shown in FIG. 9.

In one embodiment, article 100 comprises a film or sheet that isextruded through at least one die having a face having a texturecorresponding to the desired texture for article 100. Texture 130 istransferred from the die face to article 100 during extrusion. Inanother embodiment, texture 130 is either compression molded orinjection molded onto surface 120 of article 100 to produce a textured,low-wettability surface 120 on article 100. A mold having at least oneface comprising texture is used to impart corresponding texture 130 tosurface 120 of article 100 during the molding process.

In another embodiment, a plurality of nanoparticles is combined or mixedwith a ceramic precursor such as, but not limited to, polysilazaneprecursors to form either a slurry or suspension of nanoparticles in theceramic precursor. The slurry (or suspension) is then applied to asurface of an article by means that are well known in the art, such asspraying, spin coating, painting, dipping, and the like. The coatedarticle is then heated to convert the ceramic precursor into a ceramic,such as, but not limited to an oxide, carbide, nitride, silicide, orcombinations thereof, thereby forming a textured, low-wettabilitysurface comprising the plurality of nanoparticles embedded in a ceramiccoating. Such heating may involve calcining the ceramic precursor orheating under a reactive atmosphere. The resultant surface may be usedin applications such as icing resistant coatings for aircraft turbines,where stability at high temperature is desired.

Additionally, surface 120 may be formed by vapor-based depositiontechniques such as, but not limited to, PVD, LPCVD, CVD, PECVD, andcombinations thereof.

Moreover, in some embodiments, the forming step is accomplished bychemically forming the features 130 onto the substrate 110. In certainembodiments, this is accomplished by manipulating the surface chemistryof the material to form one or more discrete chemical phases on thesurface, for example via such well-known techniques as molecularself-assembly, crystallization, or other processes known to induce aphase separation on the surface. In other embodiments, chemical etchingmay be used by applying an etchant to the substrate. The etchant maycomprise an acid, a base, a solvent, or other agent with suitableproperties to react with the substrate to form features on the surface.

Where the reference liquid (i.e., the liquid for which the surface ofthe article shows low wettability) is water, the superhydrophobic natureof surface 120 makes it suitable for a number of applications thatrequire resistance to fogging, soiling, contamination, and icing.Article 100 having surface 120 may also be used in applications in whicha surface having low-drag, self-cleaning, and heat transfer propertiesare desirable.

In one embodiment, the surface 120 primarily provides article with anincreased resistance to “icing:” the formation and accretion of icethrough deposition and freezing of supercooled water droplets on asurface. In this embodiment, article 100 is an airfoil 1000, such as,but not limited to, aircraft wings, propellers, low pressure compressorand fan components of gas turbine engines, wind turbine blades, andhelicopter blades—articles that are particularly susceptible to icingunder certain conditions. A schematic representation of a cross-sectionof an airfoil having a low-drag icing-resistant surface is shown in FIG.10. As seen in FIG. 10, airfoil 1000 has an icing-resistant surface1020, as described herein, disposed on its leading edge 1010. In anotherembodiment, article 100 is a component of a turbine assembly, forexample, a gas turbine aircraft engine, schematically shown in FIG. 11.Article 100 includes components of turbine assembly 1100, such as inletguide vanes (IGVs) 1110, rotors, stators, struts 1120, temperature andpressure sensors located in the flow path, fan blades 1130, fan outletguide vanes (OGVs) 1160, spinners 1170, and other surfaces that accreteice under icing conditions. It is noted that the operating principlesand general structure of turbine assemblies and airfoils are well knownin the art and are not repeated herein. Incorporation of surface 120into any of the aforementioned articles enables any accreted ice to beshed before attaining a mass that is sufficiently large to impede thefunction of article by, for example, flame out or stall. In many cases,such structures benefit from the low-drag properties of surface 120 aswell.

Due to the high contact angle on a superhydrophobic surface, the wateron surface 120 forms small droplets and rolls off instead of sheeting,and the droplets carry away dirt particles along with them, thus leavinga clean dry surface. In situations such as fogging of a surface, smalldroplets formed by processes such as condensation deposit on the surfaceand reflect the light, thus making the surface “fog.” Because of thehigh contact angle 140 between the condensed droplets and surface 102,the droplets do not adhere to surface 120, but instead roll off.Accordingly, article 100 is resistant to such fogging. In oneembodiment, article 100 is either transparent or translucent. Examplesof article 100 in which surface 120 serves primarily as a self-cleaning,anti-fogging surface include lighting products, automotive products(such as headlamps, windows, and mirrors) building components (such asglass panes, windows, and mirrors), lenses, video displays and screens,and the like.

In one embodiment, the low-drag properties of surface 120 can be adaptedto facilitate the transport of fluids, such as crude oil, water, and thelike, through long pipelines. The friction within a pipeline typicallyleads to significant pressure drop. To overcome such a pressure drop,greater power is required to pump the fluids. Accordingly, article 100may be a pipe, conduit, or the like, for conducting fluids and gases,having surface 120 is disposed within the pipe along the path of thefluid or gas; i.e., inside the pipe. Surface 120 with texture 130 willreduce the friction between fluid and the wall of pipe. Consequently,the power required to pump the fluid through the pipe will besignificantly reduced.

Reduction of hydrodynamic drag has always been a priority for marinevessels. Increased drag not only increases the fuel consumption of theship, but also is harmful to the environment due to larger amounts ofemissions. Fouling of watercraft hulls by marine organisms is a primesource of increased drag. In yet another embodiment, the low-drag andself-cleaning properties of surface 120 can be adapted to reduce foulingand friction between water and a hydrodynamic body. Significant amountsof energy are required to overcome friction due to water. Such bodiesexperience significant flow friction from the water. Thus, article 100may include various watercraft, ranging from ocean-going vessels andsubmarines to small sailboats and canoes. While hulls and other surfacesare shaped in such a way to reduce friction, additional reductions inskin friction may be obtained by providing the hull with surface 120 inaccordance with embodiments of the present invention. Moreover, thelow-wettability surface prevents marine organisms from adhering to thesurface of a watercraft.

In another embodiment, the low-drag and self-cleaning properties ofsurface 120 can be adapted to fabrics for use in garments, furniture,hospital equipment, and the like. For example, article 100 may includeclothing used in sports such as swimming, track and field, andbicycling. In another example, article 100 includes fabric upholsteryand bedding having surface 120, thus utilizing the self-cleaningcapability of surface 120. In such applications, at least onesuperhydrophobic film or coating in accordance with embodiments of thepresent invention may be applied to a surface of the article.

The self-cleaning properties of surface 120 are also useful in otherapplications. Accordingly, surface 120 may be incorporated into varioushousehold appliances, such as refrigerators, dishwashers, ovens, rangesand the like.

Surface 120 may be used in heat transfer applications, such as, but notlimited to, heat exchangers, cooling towers, and otherthermal-management systems, that rely on a phase change (e.g., boiling).Air bubbles on the texture of surface 120 nucleate at a higher rate thanon a nominally a flat surface, facilitating heat transfer through thephase change and bubble formation and migration.

While typical embodiments have been set forth for the purpose ofillustration, the foregoing description should not be deemed to be alimitation on the scope of the invention. Accordingly, variousmodifications, adaptations, and alternatives may occur to one skilled inthe art without departing from the spirit and scope of the presentinvention.

1. An article comprising: a surface disposed on a substrate, wherein thesurface comprises a. a material having a nominal liquid wettabilitysufficient to generate, with a reference liquid, a nominal contact anglein a range from about 60° to about 90°, the material comprising at leastone material selected from the group consisting of a polymer and aceramic; and b. a texture comprising a plurality of features; whereinthe surface has an effective liquid wettability sufficient to generate,with the reference liquid, a contact angle in a range from about 120° toabout 180°.
 2. The article according to claim 1, wherein the surfaceconsists essentially of the material.
 3. The article according to claim1, wherein the material is selected from a group consisting essentiallyof polycarbonates, polyimides, polysilazanes, acrylates, polyurethanes,epoxies, polyether imides, polysulfones, block copolymer/copolymermixtures, and combinations thereof.
 4. The article according to claim 1,wherein the material comprises a ceramic.
 5. The article according toclaim 4, wherein the ceramic comprises a ceramic selected from the groupconsisting of an inorganic carbide, an inorganic oxide, an inorganicnitride, and combinations thereof.
 6. The article according to claim 5,wherein the ceramic comprises a ceramic selected from the groupconsisting of tin oxide, titania, silicon carbide, titanium nitride,stibinite, zirconia, hafnia, titanium oxynitride, and combinationsthereof.
 7. The article according to claim 1, wherein the texturecomprises a plurality of features, wherein each of the plurality offeatures has a dimension in a range from about 10 nm to about 50,000 nm.8. The article according to claim 7, wherein the dimension is in therange from about 10 nm to about 10,000 nm.
 9. The article according toclaim 8, wherein the dimension is in the range from about 10 nm to about1000 nm.
 10. The article according to claim 7, wherein the plurality offeatures are spaced from each other by a spacing dimension, wherein thespacing dimension is substantially equal to the dimension.
 11. Thearticle according to claim 7, wherein the plurality of features aresubstantially close-packed.
 12. The article according to claim 7,wherein the plurality of features comprise at least one of bumps, cones,rods, wires, channels, substantially spherical features, foamedstructures, substantially cylindrical features, pyramidal features,prismatic structures, and combinations thereof.
 13. The articleaccording to claim 7, wherein the plurality of features is arranged inan ordered array on the surface.
 14. The article according to claim 7,wherein the plurality of features is sprayed onto the substrate.
 15. Thearticle according to claim 7, wherein the plurality of features isstamped onto the surface.
 16. The article according to claim 7, whereinthe plurality of features are chemically formed on the substrate. 17.The article according to claim 1, wherein the article further comprisesa bulk portion disposed beneath the surface, and wherein the pluralityof features of the texture of the surface extends into a bulk portion ofthe article.
 18. The article according to claim 1, wherein the articleis one of an airfoil, a turbine component, a heat exchanger, awatercraft hull, an appliance, and a fabric.
 19. The article accordingto claim 16, wherein the article is an airfoil and the surface isdisposed on at least a leading edge of the airfoil.
 20. The articleaccording to claim 1, wherein the reference liquid comprises water. 21.The article according to claim 1, wherein the reference liquid comprisesat least one hydrocarbon.
 22. An article comprising: a surface disposedon a substrate, wherein the surface comprises a. a material having anominal wettability sufficient to generate, with water, a nominalcontact angle in a range from about 60° to about 90°, the materialcomprising at least one material selected from the group consisting of apolymer and a ceramic; and b. a texture comprising a plurality offeatures; wherein the surface has an effective wettability sufficient togenerate, with water, a contact angle in a range from about 120° toabout 180°.
 23. A method for making an article, the method comprising:a. providing a substrate and b. forming a surface on the substrate,wherein the surface comprises a material having a nominal liquidwettability sufficient to generate, with a reference liquid, a nominalcontact angle in a range from about 60° to about 90°, the material,comprising at least one material selected from the group consisting of apolymer and a ceramic, and the surface further comprising a texture,wherein the texture comprises a plurality of features; wherein thesurface has an effective liquid wettability sufficient to generate, withthe reference liquid, a contact angle in a range from about 120° toabout 180°.
 24. The method according to claim 23, wherein formingcomprises spraying the plurality of features onto the substrate.
 25. Themethod according to claim 23, wherein forming comprises stamping theplurality of features onto the substrate.
 26. The method according toclaim 23, wherein forming comprises chemically forming the features ontothe substrate.
 27. The method according to claim 26, wherein chemicallyforming comprises at least one operation selected from the groupconsisting of a. forming at least one discrete chemical phase on thesurface of the substrate, and b. chemically etching the substrate usingat least one etchant selected from the group consisting of an acid, abase, and a solvent.